The present invention relates generally to a separator for fuel cells, and more particularly to a separator used between unit cells in a fuel cell built up of a plurality of unit cells connected together, each with electrodes located on both sides of a solid polymer electrolyte membrane.
Briefly, a fuel cell is a device wherein fuel (a reducing agent) and oxygen or air (an oxidizing agent) are continuously supplied to it from outside for electrochemical reactions through which electric energy is taken out, and classified depending on its working temperature, the type of the fuel used, its applications, etc. Recently developed fuel cells are generally broken down into five types depending primarily on the type of the electrolyte used: a solid oxide type fuel cell, a melt carbonate type fuel cell, a phosphoric acid type fuel cell, a solid polymer electrolyte type fuel cell, and an alkaline aqueous solution type fuel cell.
These fuel cells use hydrogen gas resulting from methane or the like as fuel. More recently, a direct methanol type fuel cell (sometimes abbreviated as DMFC) relying on direct use as fuel of a methanol aqueous solution has been known in the art, too.
Among others, attention has now been directed to a solid polymer type fuel cell (hereinafter also abbreviated as PEFC) having a structure wherein a solid polymer membrane is held between two catalysts and these components are further sandwiched between a gas diffusion layer (GDL) and separators.
To get around leakage problems with this PEFC, for instance, to prevent the fuel and oxidizing agent gas feeds from leaking out or being mixed, gasket members are located in such a way as to sandwich the polymer electrolyte membrane between them around the electrodes and these components are held between the separators (JP-A2005-191002).
For the separators, moldings comprising carbon and resins or metal materials coated with a metal thin film of high corrosion resistance are used (JP-A2005-2411).
With the gasket members separate from the separators, polymer electrolyte membranes and electrodes, however, there is a problem in that the assembly work efficiency of unit cells using these components goes worse.
There are some limits to making separators comprising moldings thin, and with separators comprising a metal material coated with a noble metal thin film of high corrosion resistance such as a gold one, there is a problem in that the metal material is exposed in section, rendering cracks likely to occur at the interface between the metal material and the metal thin film.